1. Field of the Invention
The present invention relates to a resin-formed substrate in which a metal frame patterned in shape of a circuit pattern by press working, etching, or the like is encapsulated with a resin.
2. Related Background Art
In recent years, there are growing demands for miniaturization and extension of functionality of electronic equipment, and technological development is under way toward miniaturization and higher performance of printed circuit boards. Research is being made in high density mounting based on realization of multilayer structures of printed circuit boards and thinner line structures of wiring patterns, and miniaturization is also under way for electronic components themselves to be mounted on the boards. There has been a growth in use of the surface mounting type without leads.
On the other hand, in the case of the printed wiring boards in the field of electronic equipment working with a large electric current like a large inverter control circuit or a primary power circuit, the circuit pattern is formed of a very thin copper foil in the thickness of 0.18 to 0.7 xcexcm on a glass fabric based epoxy resin or paper based phenolic resin. For this reason, the area of the circuit pattern has to be increased in order to increase the current capacity, and electronic components and wiring patterns have to be set apart from each other over a certain distance in order to ensure sufficient reliability of electrical insulation. These were the hindrance to the development of high density mount technology and delayed the miniaturization of the printed circuit boards with such a large current control as the large inverter control circuit or the primary power circuit, which resulted in hindering the miniaturization of electronic equipment.
Furthermore, the printed circuit boards with the large current control as described above often carry large and heavy electronic components such as inductors, relays, and the like, and frequently suffer such failure that lands (electrode portions) of the printed wiring board with electronic components soldered there are peeled off because of vibration or the like. For securely fixing the electronic components on the printed board, it is possible to use an adhesive. However, this method requires a production process except for soldering and use of the adhesive in addition to solder, which largely increases the processing cost. Therefore, it was not practical.
In order to achieve the miniaturization while overcoming the above problem, there are proposals on a resin-formed substrate such as a resin-molded substrate in which a metal frame having a circuit pattern formed therein is coated with a resin, as described in Japanese Patent Application Laid-Open No. 2000-133897. The resin-formed substrate is formed in such a way that a thin plate of copper-or brass normally about 0.5 mm thick is processed in shape of a desired circuit pattern by press working or etching to obtain a metal frame and that the metal frame is encapsulated with a resin about 1.0 mm thick by insert molding. Since the thickness of the thin plate of copper or brass allowing flow of electric current is larger than those of the ordinary printed wiring boards, it is feasible to construct the large current circuit pattern of a finer pattern and achieve higher density of the circuit pattern. The substrate is also excellent in electrical insulation, because the metal frame is coated with a resin. Accordingly, the substrate of this type is particularly effective to construction of the primary electronic circuit pattern board working with the alternating current of high current intensity like the inverter circuit such as the power circuit pattern or the like.
The injection molding machine with high production efficiency is used in the resin molding for coating the metal frame, and the resin material is normally PPS (polyphenylene sulfide) or PBT (polybutylene terephthalate). Since the metal frame has the lands (electrode portions) for the electronic components to be connected and soldered at predetermined positions, circularly opening land apertures for exposing the lands are provided in the surface of the resin-formed substrate.
A flow soldering technique of implementing soldering with molten solder is used as a method of soldering the electronic components to the resin-formed substrate. The flow soldering technique is a method of blowing the molten solder off over a solder bath, transporting the resin-formed substrate with the electronic components mounted thereon, to over the solder bath, and bringing a solder side as a back surface of the resin-formed substrate into contact with the molten solder blowing off, thereby soldering the leads from the electronic components. In this method, a flux is preliminarily applied onto portions subjected to soldering on the resin-formed substrate, in order to achieve good soldering of the components to the resin-formed substrate. The flux is applied using a flux applying device called a fluxer. Many resin-formed substrates are planar, and the flow soldering technique is normally used for the soldering thereof.
However, while the electronic components are soldered to the resin-formed substrate by the flow soldering technique, the resin-formed substrate is heated only on the solder side thereof by the molten solder blowing off. The resin-formed substrate has a component side for mounting the electronic components thereon, and a solder side for soldering the electronic components thereto, and each of the two sides is coated with a resin about 1.0 mm thick. For this reason, heat on the solder side is hard to transfer to the component side, so that a temperature difference is made between the component side and the solder side. This posed a problem that the resin-formed substrate was warped. This deformation raised significant influence, particularly, when the resin-formed substrate had a large area.
In addition, the resin-formed substrate is difficult to print a component silk thereon, unlike the ordinary printed wiring boards. Therefore, in a step of mounting the electronic components on the resin-formed substrate, it is difficult to specify mounting positions of the electronic components. This might cause mounting of the electronic components at incorrect positions or require a lot of time for specifying the mounting positions, which heavily lowered workability.
In order to achieve secure soldering in the aforementioned flow soldering technique, it is important to preliminarily even the lengths of the leads of the electronic components projecting on the solder side. However, since the lengths of the leads of the electronic components mounted on the resin-formed substrate are different depending upon types and sizes of the electronic components, the leads of the electronic components have to be preliminarily cut in predetermined length before the components are mounted on the resin-formed substrate. The lead cut operation of preliminarily cutting the leads according to the lengths of the leads for the respective electronic components, however, increases the production cost of the resin-formed substrate.
The electronic components can also include a component to which the lead cut operation is applicable with difficulty, e.g., a large electronic component like an interlock relay for large electric current. In this case, it is necessary to provide a space between the electronic component and the resin-formed substrate, to place an insulator between the electronic component and the resin-formed substrate, or to design the mount position of the electronic component on the resin-formed substrate so as to take a long creepage distance for insulation equivalent to the lead cut length. These countermeasures all result in failure in secure mounting of the electronic component, increase in the production cost, and hindrance to the miniaturization of the resin-formed substrate, however.
Meanwhile, in the case where a relatively large component, e.g., an inductor of large diameter, had to be mounted on the resin-formed substrate, it was mounted while lying on its side so as to keep the center of gravity of the inductor low, in order to fix it on a stable basis. However, the component mounted while lying on its side occupied a large area on the resin-formed substrate to hinder the miniaturization of the resin-formed substrate. For mounting the component in the vertical orientation in order to keep down the area on the resin-formed substrate, it is also conceivable to use an adhesive or the like to fix the component. This method, however, requires a production process except for soldering and the adhesive except for solder, thus largely increasing the processing cost.
It is, therefore, an object of the present invention to provide a resin-formed substrate that makes it possible to suppress occurrence of the warp of the substrate due to the temperature difference between the solder side subjected to soldering, and the component side, without increase in production cost.
Another object of the present invention is to provide a resin-formed substrate that permits secure soldering, regardless of lengths of leads of electronic components to be mounted.
Still another object of the present invention is to provide a resin-formed substrate that makes it feasible to readily specify a mounting position of each electronic component by means of a rib.
According to a first aspect of the present invention, there is provided a resin-formed substrate in which a metal frame forming an electronic circuit pattern is coated with a resin and which comprises a component side for mounting an electronic component thereon, and a solder side for soldering thereto a lead extending from the electronic component, which is the reverse to the component side, wherein the component side is provided with a rib formed of a resin.
In the resin-formed substrate in accordance with the present invention, it is preferred that the rib has an elongated shape extending in a direction perpendicular to an injecting direction of the resin at the time when forming the resin-formed substrate by insert molding.
Further, it is preferred that the rib is formed so as to contour the electronic component to be mounted on the component side.
Moreover, it is preferred that the rib is a seat for the electronic component.
Further, it is preferred that an electrode for mounting the electronic component thereon, and a lead through hole for allowing the lead therethrough to project on the solder side of the resin-formed substrate are formed inside the rib.
Moreover, it is preferred that the height of the rib is adjusted so as to even the lengths of all the leads of the electronic components to be mounted on the resin-formed substrate, projecting from the solder side of the resin-formed substrate.
Further, it is preferred that at least two of the ribs are formed continuously in the direction perpendicular to the conveying direction of the resin-formed substrate at the time when carrying out the flow soldering of the resin-formed substrate.
According to a second aspect of the present invention, there is provided a resin-formed substrate unit comprising the resin-formed substrate and an electronic component mounted on the resin-formed substrate.
In the resin-formed substrate unit in accordance with the present invention, it is preferred that the electronic component is a vertical inductor.
Further, it is preferred that the electronic component is a large relay.